Cancer is a life-threatening medical condition that is deserving of serious scientific and medical investigation with a view to finding improved curative treatments. Breast cancer is the most frequent form that occurs in women. Other common susceptible sites in the abdomen—affecting both men and women—are the kidney, liver, colon and stomach.
Two broad categories of cancer treatment are: direct surgical manipulation on the affected tissue and non-invasive treatment. Non-invasive techniques utilise modalities such as X-rays, lasers, microwave, hyperthermia, cryoablation etc., the selection of which depends upon the stage, size, shape and position of the target area. Ultrasound is known to be useful as one form of hyperthermia. Single focused transducers, however, are not very flexible in creating a desired spatial distribution of ultrasound energy within the treatment field. This is because they have a fixed focal depth and frequency of operation. Also, the size of the focal region may not match the size of the tumour. To treat the whole abnormal region, an ultrasonic beam needs to be mechanically scanned over the target area Besides this, the residual amount of energy residing in dispersion zone and its overlap during scanning over the target region may result in undesirable hot-spots in the overlying normal tissue.
High Intensity Focused Ultrasound is a non-invasive technique capable of selective destruction of tissue volumes within the body. The aim is to produce damage in the focal region of an acoustic beam in a predictable and reproducible manner, while sparing overlying and surrounding tissue. A specific multi-probe technique, such that the individual probes are excited in unison, at comparatively low power levels, is known.
One example of this known approach—for use in the treatment of brain cancers—is described in the publication: Chauhan, S, Davies, B. L., Lowe, M. J., ‘A Multiple Focused Probe System for HIFU-based Neurosurgery’, Ultrasonics, vol 39, 33-44, 2001. This approach, as outlined in the publication, is not directly applicable to the treatment of abdominal and breast cancers. There are important anatomical differences between the human torso and head, most notably the bone enveloping the brain. As such, no immediate acoustic window to the brain is available without removing a section of the skull. This limits the ability to manipulate the orientation of the ultrasonic transducers. In the abdomen, it is the ribs that pose obstacles to an acoustic window, however there are interstices between the ribs that make orientation of the ultrasonic probes easier.
It is an object of the present invention to provide a form of focused ultrasonic treatment of cancers that seeks to improve the efficacy of such a modality, and reduce the unwanted damage to normal tissue.